/ Sleeping on Snow

I'm forever seeing pics of manly men battling their way up brutal alpine routes or FAs in the Greater Ranges, and they all seem to have closed cell sleeping mats strapped to the outside of their packs. Is this to be used in conjunction with an inflatable for extra warmth, or on its own?

If on its own, is this just a weight saving thing, shaving off the grams in exchange for being a wee bit chilly?

In reply to alexm198:
You do know that snow is a good insulator?
"Ten inches of fresh snow with a density of 0.07 inches, seven percent water, is approximately equal to a six-inch-layer of fiberglass insulation with an insulation R-value of R-18."

In reply to alexm198: Stand on your thermarest with your crampons on and you're in for a cold night. Stand on a karrimat with your crampons on and it's not such a show stopper. Biving on tiny icy ledges is a mere at the best of times hard not to stand on things. Also thermarests are a bit sliddy.

Concentrate on the density of 7% water (density in g/cm^3), meaning the snow pack is mostly air. Air is a good insulator, so a bed of dry snow won't feel that cold. This is one reason why no-one clears their roof in alpine resorts; the snow is good insulation. It's also one reason why melting snow is hard, and why it's best to start with some water in the pot (the energy required to change state from solid to liquid is the other main reason).

Compacted or wet snow will have a higher density, and conduct heat better.

I think it's because of all the pointy things. I had a rather sleepless winter ml assessment when i managed to slice my thermarest with a saw (idiot i know). I spent 2 nights snow holing lying on my rope/rucksack/inlflated dry bags/food/poo pot begging the other guy not to mention it to the assessors till the results were in!

> Compacted or wet snow will have a higher density, and conduct heat better.

i.e. when you have lain down on it! So bury a water bottle in fluffy snow and it will probably not freeze over night, but try lying in snow and you get cold bloody fast.

Alex, I was sleeping out last night at -20: two mats, a Z-rest and 3/4 length ultralight thermarest - empty pack goes under my feet to they have two layers as well. It works well, never any cold from below, and if the thermrest punctured, the z-rest gives quite a lot of insulation on its own although I've never have punctured one.

In reply to alexm198: Punctured a thermrest with crampons, silly mistake and thankfully in the morning I was leaving. Saying that, I was careless and repair kits are easy enough to carry.

I recently bought a multimat Exped mat (foam) and it's LOADS warmer than my thermarest. I know you can get warmer thermarests but the multimat is in a different league. I'll use both together when car camping (for extra comfort and luxury!), but will just take foam mat for everything else. I guess having it strapped to the outside of the pack for walk-in's etc is an advantage as well, no need to worry about it getting damaged then either. Also I forgot how nice it was not to have to inflate or pack a thermarest away, and to not slide off the darn thing through the night!

Bought a Thermarest Xtherm recently. Amazing. Miles lighter, smaller and warmer than my thermarest prolite 4, comes with free repair patches and isn't that crinkly (like the summer version is famous for. I've used it on snow directly and was toasty.

for nasty crazed stuff where a puncture is a game-ender then i take a thermarest with either a slab of z-lite or a sheet of 2mm astro foam with a silver facing if its warmer than about -5c. this system packs tighter and still handles if punctured and combined with a pack and the rope. ropes, when coiled large and laid under other insulation actually insulate really well (on sleepless nights ive contemplated a special bag it would go in to make an intentional system...).

for valley-based stuff or where its just a night or two and/or the chance of puncture is minimal (ie not on cramped ledges etc) then an exped down mat is unbeatable. straight onto snow at -22c is taken for granted, tho a ground sheet or tent floor helps with moisture. only issue is they dont fit inside bivvy bags well. the x-therm does the same job with more noise.

a while back radson mentioned the nemo zor in a similar post. ive got 2 3/4 sized ones that combine well for serious cold, or alone to about -3c. they fold no smaller than an exped tho. for real cold they are a good option as still smaller than a foamy and hopefully less chance of puncturing 2 (...?).

if you do stick with the old school single-big-foamy; rolled up on your pack is a pain in the ass. modify it to fold concertina-style, or roll loose and line your pack with it.
a good system ive seen in japan is a z-lite (made of dimply foam) inside an astro foam sleeve.

another option still is a klymit mat (skeleton of an inflatable) inside the astro foam sleeve.
id keep an eye on that company as i dont doubt sooner or later a down filled version will arise (they are currrently messing about with argon inflation...)

In reply to Pritchard: X-therm does look good. It'll be a LONG time before I consider spending that sort of money on a sleeping mat again though! Kind of like the simplicity of the foam mat as well to be honest, cheap, reliable and does the job. Bit like me

In reply to alexm198: not having done any 'brutal' alpine routes I cannot speak for the manly chaps you have been looking at. What I have used successfully on the col du midi is a similar system to Dr Archer although with a full length ultralight thermarest instead of a 3/4 on a blown foam under mat. Slept like a baby in my me lightline. Never managed to puncture the thermarest, and thinking about it now is a minor miracle as I tend to act before I think.

> (In reply to alexm198)
> You do know that snow is a good insulator?
> "Ten inches of fresh snow with a density of 0.07 inches, seven percent water, is approximately equal to a six-inch-layer of fiberglass insulation with an insulation R-value of R-18."

But snow is cold, it conducts lots of heat. It would not offer any insulation value by lying on it, surely? Hence the mat.

In reply to Lukeva:
The mat you carry up in -35° is also cold until you warm it up, itīs a question of how fast it lets the heat escape from your body. Exactly the same as with snow which is infinitely better than rock, earth, metal, concrete, ice, water etc. But you need to ensure the snow doesnīt start melting so something else in between you and the snow is desirable. Even compacted dry snow has a suprisingly high insulation value (ca 0.5W/m/K) which is how Eskimos survive nicely.

> Exactly the same as with snow which is infinitely better than rock, earth, metal, concrete, ice, water etc.

Careful with that hyperbole, Eugene...

Snow will be a better insulator than rock, soil, metal, etc, but it will still conduct heat away, so not infinitely better...

I'm not suggesting that sleeping directly on snow is a great idea, just pointing out that it's not as bad as you might think, since even compacted snow is a reasonable insulator compared to other materials you might sleep on at the same temperature.

Fresh snow will compact if you lie on it. Consolidated, re-frozen pack snow won't compact anywhere near as much; that's why you can walk on the stuff without sinking in.

In reply to alexm198: When sleeping on a glacier, I used to have a full-length mat, a 3/4 length thermarest and put a fleece under my sleeping bag, where my hips were. That's where most of my weight seemed to be pressing down.

Also, I found it best to use my goretex jacket and down jacket on top of my sleeping bag as another layer. Using a down jacket like this is a lot better than wearing one in a sleeping bag.

If you have a decent sleeping bag you can sleep quite well at very low temperatures on snow by putting all your spare clothes and gear, ropes, slings, rucksack, anything soft, and so on under you. Some kind of karrimat (closed cell) is nice but it's a luxury.

Better still is if you can find an area of sandy gravel, on a moraine or ledge. The coldest is on ice as it conducts better. Make sure that if you don't have double boots you don't leave your boots to freeze solid outside your sleeping bag. If you have double boots use the inners as a pillow so they help insulate and don't freeze either. It's quite possible to sleep happily if you are methodical.

In reply to jimtitt: Have you read Murray's "Mountaineering in Scotland"? I remember a funny section on things they tried using as early versions of sleeping mats, but they were clearly aware of how much difference some decent insulation under you makes!

I rarely used any form of mat, simply because of the volume question, and I did a lot of bivouacking up to about 6000 m, often on snow. The coldest was in winter in Bolivia, still just putting clothing, ropes etc under you was all we did. I had a good Point 5 double sleeping bag though but the person I bivouacked with had a fairly light sleeping bag. A decent small tent or double bivvy bag is important too.

I was just reading Murray's book and the experiments with tarry paper but one big difference is that they didn't have modern down gear.

In reply to alexm198:
Decent exped carrimat, much lighter and much more reliable than a thermarest. Also cheaper, the only disadvantage is that they're bulky, I don't find inflatable mats to be comfortable but maybe that's just me. I slept in a ice cave on the mat, in a goretex bivi bag and -20c bag sleeping bag, wearing full clothing and a down jacket inside the bag. I think the down jacket made things worse, I should of put it over my head or something. I wouldn't like to bivi for more than one night in a row in the cold and damp!